Shani Wallis, Editor

The Seymour-Capilano twin tunnels contract in Vancouver, Canada, is terminated and the process to appoint a replacement contractor to complete the works is underway.

In a statement yesterday (Tuesday, 27 May), Metro Vancouver, the regional utilities provider, said that by refusing to continue work on the Seymour-Capilano tunnels Bilfinger Berger (Canada) Inc. had forfeited its right to perform further work on the project and had forced termination of the contract. The Canadian division of Bilfinger Berger of Germany brought the two tunnel headings to a standstill in early January when a zone of weak rock raised concerns for worker safety.

The lead heading was 4.1km or 57% into its 7.1km long drive when it was stopped on January 7th. The second was at 3.8km or 55% through the parallel tunnel when it was halted on January 10th. The two 3.8m diameter Robbins TBM headings were just past the deepest part of the alignment and under a cover of between 500m and 550m when they came to a stop.

It is reported that ten rock fall events were reported by Bilfinger Berger to the health and safety authority in January and that it was WorkSafe BC that closed down excavation until the safety hazard was resolved.

Doug Neden, Project Manager for Metro Vancouver's Greater Vancouver Water District, told TunnelTalk in a telephone interview in late April that it was said to be a combination of the rock's weakness and the release of in-situ stresses that caused rock falls from the crown. He said that although the term 'rockbursting' had been used, there had been no explosive spalling or slabbing of the rock. "The signs of stress relief are evident in the profile just off the vertical, at the 11 o'clock and 5 o'clock marks," he said. "Had the rock been stronger, it is said the falls would not have occurred."

Conditions were said to be stable since the lead TBM was stopped in early January. The second TBM in the parallel drive, about 100m distant and about 300m behind, was stopped before it entered the weaker zone.

Metro Vancouver said that its tunnel designer and construction supervision engineer Hatch Mott MacDonald had prepared a plan that addressed the safety concerns and allowed for safe resumption of work. Bilfinger Berger did not accept the plan and high-level talks between contractor, client, designer, WorkSafe BC, and the client's overall program and construction manager Pacific Liaicon/SNC Lavalin, failed to resolve the stalemate.

Development of the plan included Robbins since technical solutions involved modification of the machines. The 3.8m diameter tunnels for example, limit bolt holes and bolt lengths without using couplers. A larger diameter would allow for longer bolts but would require modification of the machines in-situ.

In the TunnelTalk interview Neden confirmed that 40m long probe holes drilled into the face of the lead heading had been surveyed with endoscope cameras but that these had provided little useful indication of conditions ahead. After stopping excavation, the front 60m of the lead heading was taped off for safety and crews applied shotcrete to the tunnel walls behind.

In its statement Metro Vancouver said that "the world's foremost experts in rock mechanics and tunnel engineering" endorsed the plan as "safe and viable" and that Bilfinger Berger's claims "are without merit". In the statement Johnny Carline, Chief Administrative Officer for Meter Vancouver, said "Bilfinger Berger's refusal to move forward.......is a great frustration" adding that "the contractor has provided us with no practical alternative in terms of completing the work".

Bilfinger Berger has not been available for comment or interview.

The contract's GBR (geotechnical baseline report), prepared by Hatch Mott MacDonald and project geotechnical engineers Golder Associates, predicts granite/granodiorite bedrock of 80-285MPa with an RQD of generally more than 75% for the majority of the twin 7.1km drives. The maximum 640m deep alignment between the 180m deep access shaft at Seymour and two 275m deep x 4m diameter raisebores at the Capilano end, is determined by the need to pass beneath two glacial valleys infilled with waterbearing sediments.

Geological section of the 7.1km alignment

The tunnels are designed to remain largely unlined with support behind the two Robbins High Performance main beam gripper TBMs comprising mainly rock bolts and wire mesh with shotcrete as needed and steel sets provided for the worst Class 5 conditions. Sets were not being installed when the lead TBM stopped. Water ingress, a major concern in the two 2.3% down gradient TBM tunnels working from the single 180m deep x 11m diameter access shaft, was said to be lower than anticipated at 16- 18litres/sec.

Suspension of tunnelling caused layoff of some 30 tunnel workers, many brought in by Bilfinger Berger from the Philippines for the contract.

The two tunnels are part of GVWD's $Can600 million water supply upgrade. One tunnel brings raw water from the Capilano reservoir for treatment at the new central treatment plant at the Seymour reservoir. The other returns treated water to Capilano for feeding into that area's distribution network. According to Neden, the new treatment plant is more than 90% complete and will go on-line in December 2008 as scheduled. "Operation of the plant is not dependent on completion of the tunnels," he told TunnelTalk. "The tunnels were always scheduled to come on-line after the treatment plant."

Bilfinger Berger was awarded the twin tunnels contract in August 2004 after submitting the lowest of three bids. Its $Can99.65 million bid, was below the Engineer's Estimate and more than $Can86 million below the second bid. The contract is now reported as a $200 million project.

Early delays excavating the 180m x 11m diameter access shaft set the contract back by more than six months. Subsequent delays launching the TBMs and downtime to install water control sumps and replace motors and gearboxes on the machines had the 49.5-month contract running up to a year behind schedule before tunnelling halted in January. Rock conditions in the shaft and the impact on excavation was the first issue heard by the contract's dispute review board (DRB).

Bilfinger Berger had planned average rates of 28m/day working 24h/day, 7 days/week to complete both tunnels in about 12 months. The machines had recorded rates of 20-22m and a peak of +30m in a day of two 10h production shifts and a 4h maintenance shift. The contract was originally to be completed by March 2009. There can be no reliable prediction now of when the remaining 3km+ of the two tunnels, plus the two Capilano raisebores and all finishing works, will be complete, nor how long the ensuing legal battles will take to resolve.